In recent years, there have been strong demands for a data transmission module capable of high-speed data communication with a large capacity, which is superior in space property and noise resistant property, and can be mounted on small-size, thin consumer appliances. Examples of the data communication in consumer appliances include data communication between a display and a mother board in a notebook computer and data communication between a display and a mother board in a PDA (Personal Digital Assistant). In recent years, in an attempt to achieve high-speed data communication with a large capacity in these small-size, thin consumer appliances, since data communication by the use of electric signals has limitations in the communication speed and the module space, data communication by the use of optical signals has been utilized. In the data communication by the use of optical signals, an optical transmission module that converts an electric signal to an optical signal, and transmits the optical signal has been used. With this arrangement, optical transmission among substrates in the apparatus can be executed.
The following description will briefly discuss the system of data communication utilizing the optical communication module. Here, in order to execute data communication inside an apparatus, the optical transmission module is supposed to have a structure in which one end of the optical transmission module is mounted on a substrate A, with the other end of the optical transmission module being mounted on a substrate B. Moreover, the following explanation will be given by exemplifying a transmission path for transmitting an optical signal as an optical waveguide.
First, an electric signal, transmitted through the substrate A, is inputted to a photoelectric conversion element (light-receiving/emitting element, optical element) a on the transmission side where it is converted to an optical signal. The photoelectric conversion element a transmits the optical signal thus converted toward an optical waveguide (optical transmission path). The optical signal, transmitted from the photoelectric conversion element a, is made incident on an incident port of an optical signal in the optical waveguide, and propagated through the waveguide. Then, the optical signal is released from a releasing port of an optical signal in the optical waveguide, and received by a photoelectric conversion element (light-receiving/emitting element, optical element) b on the light-receiving side. The optical signal, received by the photoelectric conversion element b, is converted to an electric signal, and the resulting electric signal is transmitted through the substrate B.
By electrically connecting the optical transmission module to the substrate in this manner, data communication is executed in the apparatus.
Here, conventionally, various methods for connecting an optical transmission module to a substrate have been proposed. For example, an optical transmission module described in Patent Document 1 is provided with electrode pins, and designed so that the electrode pins are secured to the substrate by soldering. FIG. 34 is a side view that shows a schematic structure of an optical transmission module 100 described in Patent Document 1. As shown in this Figure, a package 104 on which a sub-substrate 103 having an optical waveguide 101 and a light-receiving/emitting element 102 assembled therein has been mounted is provided with an electrode pin 105 that allows electrical connection to the substrate 106. Thus, since the optical communication module 100 is secured onto the substrate 106 through the electrode pin 105, data communication is available between apparatuses (not shown) by utilizing optical transmission.
Moreover, Patent Document 2 has described a structure in which an optical transmission module is connected to a substrate by using an electric connector. FIG. 35 is a side view that shows a schematic structure of an optical transmission module 200 described in Patent Document 2. As shown in this Figure, a sub-substrate 203 on which an optical waveguide 201 and a light-receiving/emitting element 202 have been mounted is provided with an electric connector 204 that allows electrical connection to a substrate 205. With this arrangement, since the optical transmission module 200 can be secured to the substrate 205 through the electric connector 204, data communication is available between apparatuses (not shown) by utilizing optical transmission, in the same manner as in Patent Document 1.    Patent Document 1: Japanese Patent Application Laid-Open “JP-A No. 2005-321560 (published on Nov. 17, 2005)”    Patent Document 2: Japanese Patent Application Laid-Open “JP-A No. 2006-42307 (published on Feb. 9, 2006)”
Here, in order to transmit an optical signal by using an optical waveguide, the incident/releasing port of an optical signal in the optical waveguide and the light-receiving/emitting element need to be properly positioned and optically coupled with each other. As described above, the light-receiving/emitting element is an element that converts an electric signal transmitted thereto from an external device through the substrate to an optical signal and transmits the optical signal, and also receives an optical signal and converts it to an electric signal. Here, in order to achieve stable data transmission, it is necessary to maintain constant the distance between the incident/releasing port of an optical signal in the light-receiving/emitting element and the incident/releasing port of an optical signal in the optical waveguide, as well as the positional relationship between the two ports.
However, the above-mentioned conventional structure has the following problems.
That is, in the structure described in Patent Document 1, the optical transmission module 100 and the substrate 106 are firmly secured to each other by soldering; therefore, for example, in a case where, upon securing the two members by soldering, a warp or the like occurs in the sub-substrate 103 or the package 104 of the optical transmission module 100, the optical transmission module 100 is secured in a deformed state, as it is. Moreover, even in a case where the optical transmission module 100 and the substrate 106 are connected to each other without any problems, since the optical transmission module 100 and the substrate 106 are brought into a firmly secured state by soldering, a deformation occurring in the substrate 106 due to an external force or the like applied thereto might be transferred to the optical transmission module 100. Moreover, since the above-mentioned structure uses solder, the optical waveguide might be deformed or damaged by influences of reflow heat.
In this manner, in a case where a deformation occurs in the sub-substrate 103 on which the optical waveguide 101 and the light-receiving/emitting element 102 are mounted, the package 104 or the optical waveguide 101 itself, since the distance between the incident/releasing port of an optical signal in the light-receiving/emitting element 102 and the incident/releasing port of an optical signal in the optical waveguide 101, as well as the positional relationship between the two ports, is changed, the optical coupling efficiency is varied to cause a problem of failure in transmitting data stably.
In particular, in a case of an optical waveguide having high flexibility, since a polymer waveguide is used in most cases, the waveguide is more susceptible to influences by heat. For this reason, it becomes very difficult to carry out data transmission in a stable manner.
Moreover, in the structure described in Patent Document 2, since an optical transmission module 200 is connected to a substrate 205 through an electric connector 204, a space used for mounting the electric connector 204 is required to cause a problem in that the entire module becomes bulky. Moreover, in a case of the connection using the electric connector 204, when the substrate 205 receives a stress in a rotation direction θ around an insertion direction (Z-axis) of the connector, the connection unit of the electric connector 204 in the optical transmission module 200 also receives the same stress, and the connection unit consequently tends to be damaged. As a result, coming off of the electric connector 204 or the like tends to occur, failing to carry out normal electrical communication to cause adverse effects in the optical transmission.
Here, specific examples of the method for connecting an optical transmission path include a method using a ferrule as a holding member and a directly pasting method onto an optical element. However, the method using the ferrule requires a space for connectors, with the result that the entire module becomes bulky. Moreover, when applied to a small-size apparatus, this structure is more susceptible to influences from vibration and impact, and deviations in the optical axis tend to occur, failing to carry out data transmission in a stable manner. In contrast, the method for directly pasting an optical transmission path onto an optical element causes a deformation of the substrate to be transferred to the optical transmission path, with the result that deviations in the optical axis tend to occur, failing to carry out data transmission in a stable manner.
In view of the above-mentioned various problems, the present invention has been devised, and its objective is to provide an optical transmission module having a small size that is capable of carrying out stable data transmission, a connection member and an electronic apparatus equipped with such an optical transmission module.